This invention relates to radial inflow turbines having a turbine wheel divided in a disc-shaped impeller element and an exducer portion, the exducer and the impeller being clamped together or otherwise connected in the axial direction of the wheel. More specifically, the invention relates to the impeller or centripetal flow accommodating element of the wheel. The exducer portion, which largely accommodates the axial portion of the flow, may be composed of a plurality of elements in the form of star-shaped discs. However, the impeller element of the invention may also be used with a conventional exducer consisting of a single, integral element.
In order to reduce cost per horsepower and improve thermal efficiency it is desirable to design radial inflow gas turbines for higher temperatures and higher peripheral speeds than what is usual today. As is known, the characteristics of the material are impaired at higher temperatures, and with higher peripheral speeds the stresses in the impeller will increase. With increasing temperature, corrosion also becomes more severe. One has previously tried to meet the more severe operational demands by the use of better materials in the turbine by cooling the blades and by improving the geometry of the turbine wheel. However, the use of high strength superalloys such as Astroloy and IN-100 has largely been limited by the restrictions of manufacturing processes with respect to the casting and forging as well as the machining of large complicated shapes. To provide cooling also causes many problems. It is therefore increasingly important to improve the basic geometry of the turbine wheel so that it will be able to withstand more severe operating conditions. The impeller element has the largest diameter and therefore the highest peripheral speed and is accordingly subjected to the highest stresses and also to the highest temperatures.